These are great ideas. I was just trying to find the things that apparently someone mentioned at Hobby Lobby (pins with numbers on them). I had thought someone said they were toys and sold at ToysRus. I did an internet search and couildn't find them. I end up using straight pins or safety pins because I don't have anything else. Recently (yesterday) I needed them. I use one pin to mark the first row, two pins to mark the second row, etc. But for this one, I only needed 8 at the most. I used safety pins once I got over 4 and I just safety pinned the pins to each other to indicate which row it was, so that on row 8, I had two large pins stuck in the first block of that row and on each safety pin was pinned 3 more pins to make a total of 8 pins.
I had another one that I just used little scraps of paper--cut them into little squares, wrote on them, 1-15 and pinned them to the top left side of the block and then threw them away at the end of the project. But I've thought it would be neat to have something a little more permanent.